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Publication Computation of viscoelastic shear shock waves using finite volume schemes with artificial compressibility(Wiley, 2025-02-03) Berjamin, Harold; European Union’s Horizon 2020The formation of shear shock waves in the brain has been proposed as one of the plausible explanations for deep intracranial injuries. In fact, such singular solutions emerge naturally in soft viscoelastic tissues under dynamic loading conditions. To improve our understanding of the mechanical processes at hand, the development of dedicated computational models is needed. The present study concerns three-dimensional numerical models of incompressible viscoelastic solids whose motion is analysed by means of shock-capturing finite volume methods. More specifically, we focus on the use of the artificial compressibility method, a technique that has been frequently employed in computational fluid dynamics. The material behaviour is deduced from the Fung–Simo quasi-linear viscoelasiticity (QLV) theory where the elastic response is of Yeoh type. We analyse the accuracy of the method and demonstrate its applicability for the study of nonlinear wave propagation in soft solids. The numerical results cover accuracy tests, shock formation and wave focusing.Publication Microstructural buckling in soft visco-hyperelastic laminates(Elsevier, 2025-02-04) Lapina, Tatiana; Xiang, Yuhai; Yao, Qi; Chen, Dean; Li, Jian; Steinmann, Paul; Rudykh, Stephan; European Research CouncilIn this work, we study the role of visco-(hyper)elasticity in the microstructural buckling of soft laminates under compressive loads. We find that the onset of buckling is related to the contrast in specific stress components; this allows us to develop analytical estimates for the critical loading. Our numerical analysis provides details on the dependence of critical strain and wavelength on the loading strain rate. We show that by activating the viscoelasticity of the stiffer layer with an increasing strain rate, one can promote the early development of the buckling (the critical strain decreases as the strain rate is increased). The tunability of the critical strain is bounded by the limits for fast and slow loading rates. Furthermore, the buckling wavelength can be tuned through strain rate variability; this effect is stronger in laminates with lower volume fractions (of stiff layer phase), while for high volume fractions, laminates tend to develop longer wavelength instabilities with diminishing tunability.Publication The Poincaré-extended 𝐚𝐛-index(Wiley and London Mathematical Society, 2024-12-20) Dorpalen-Barry, Galen; Maglione, Joshua; Stump, ChristianMotivated by a conjecture concerning Igusa local zeta functions for intersection posets of hyperplane arrangements, we introduce and study the Poincaré-extended 𝐚𝐛-index, which generalizes both the 𝐚𝐛-index and the Poincaré polynomial. For posets admitting 𝑅-labelings, we give a combinatorial description of the coefficients of the extended 𝐚𝐛-index, proving their nonnegativity. In the case of intersection posets of hyperplane arrangements, we prove the above conjecture of the second author and Voll as well as another conjecture of the second author and Kühne. We also define the pullback 𝐚𝐛-index, generalizing the 𝐜𝐝-index of face posets for oriented matroids. Our results recover, generalize, and unify results from Billera–Ehrenborg–Readdy, Bergeron–Mykytiuk–Sottile–van Willigenburg, Saliola– Thomas, and Ehrenborg. This connection allows us to translate our results into the language of quasisymmetric functions, and — in the special case of symmetric functions — pose a conjecture about Schur positivity. This conjecture was strengthened and proved by Ricky Liu, and the proof appears as an appendix.Publication Topological state switches in hard-magnetic meta-structures(Elsevier, 2024-12-07) Zhang, Quan; Rudykh, Stephan; Horizon EuropeWe propose a metamaterial design principle that enables the remote switching of topological states. Dynamic breaking of space-inversion symmetry is achieved through the intricate design of magnetic spring structures within the metamaterial building blocks, whose stiffness can be remotely altered using an external magnetic field. We develop a mathematical model to predict the magnetic field-induced deformation and tangential stiffness of the spring structure with hard- magnetic constituent phase. Building on the predictive model, we explore the necessary conditions – including the magnetization distribution and the direction of the actuating magnetic field – that enable magnetically tunable stiffness. To demonstrate the functionality of topological state switching, we apply the proposed magnetic spring to the topological metamaterial design where a tunable stiffness landscape is essential for reversible topological phase transition. Our mathematical modeling indicates that we can remotely modulate both the dispersion properties and the topological invariants (including Zak phase and winding number) of the underlying bands in the proposed metamaterial system. Finally, we show that this tunable capability extends to controlling topologically protected edge and interface states within the finite-sized metamaterial lattice. Our design strategy for the switching of topological state paves the way for the realization of smart and intelligent metamaterials featuring tunable and active wave dynamics. It also highlights the potential of magneto-mechanical coupling in the design of advanced functional materials.Publication Magnetically tunable topological states in translational-rotational coupling metamaterials(Elsevier, 2024-11-20) Zhang, Quan; Rudykh, Stephan; Horizon EuropeIn this work, an approach for engineering translational-rotational coupling (TRC) metamaterials with magnetically tunable topological states is proposed. The metamaterial exhibits diverse nonlinear mechanical behaviors, remotely controlled and activated by an external magnetic field. The design is realized through a multi-material microstructure with highly deformable hinge configurations, targeting desirable strain-softening/stiffening characteristics. This 3D-printable hinge design eliminates the complex manual assembly processes typically required in current TRC metamaterials that are based on triangulated cylindrical origami. The stiffness transition property of the TRC metamaterials can be exploited to break the space-inversion symmetry and thus achieve tunable topological phase transition. Specifically, hard-magnetic active material is incorporated to enable untethered shape- and property-actuation in these metamaterials. The TRC metamaterial design is supported by a simplified analytical model whose stiffness parameters are directly linked to the hinge microstructure, offering a significant improvement over previous empirical model. The accuracy of the analytical model is demonstrated through the comparison with the finite element and experimental results. Through these methods, the deformations induced by a magnetic field and the dynamics of superimposed waves in the TRC metamaterial system are studied. Thanks to the magneto-mechanical coupling effect, the proposed TRC metamaterial design enables remote tunability of wave dispersions and topological invariants (including the Zak phase and winding number), in contrast to existing designs that require direct mechanical loading to achieve similar effects. This tunability extends to the control of topologically protected edge and interface states within the finite system. Our findings can potentially open new ways for designing remotely reconfigurable and switchable soft mechanical metamaterials with robust wave guiding and energy harvesting capabilities.Publication Propagation of solitary waves in origami-inspired metamaterials(Elsevier, 2024-03-28) Zhang, Quan; Rudykh, Stephan; Horizon EuropeWe propose a design strategy for creating origami-like mechanical metamaterials with diversenon-linear mechanical properties and capable of remote actuation. The proposed triangulated cylindricalorigami (TCO)-inspired metamaterials enable the highly desirable strain-softening/hardening and snap-through behaviors via a multi-material and highly deformable hinge design. Moreover, we couple thesenovel non-linear mechanical properties of the TCO origami-inspired metamaterials with thetransformative ability of hard-magnetic active materials, allowing for untethered shape- and property-actuation in the developed metamaterials. We develop a mathematical modeling framework for theproposed TCO origami-inspired metamaterials, building on approximating the highly deformable hingesas a combination of longitudinal and rotational springs. We validate the accuracy of the developedmathematical modeling approach by comparing the analytically predicted compressive response of a unitcell structure with the corresponding numerical and experimental results. Using the developedmathematical modeling framework, we investigate the magnetic field-induced large deformation andsuperimposed solitary wave propagation in the TCO origami-inspired metamaterial system. We showthat the proposed metamaterial allows us to tune the key characteristics of the enabled non-linear solitarywaves, including their characteristic width and amplitude. The proposed design strategy for readilymanufacturable origami-inspired metamaterial systems paves a novel path for practical engineeringapplications. Our studies also underscore the potential of magneto-mechanical interaction in the designof reconfigurable metamaterial systems with superior non-linear mechanical and elastic wave properties.Publication Quantum advantage in information retrieval(American Physical Society, 2022-04-11) Emeriau, Pierre Emmanuel; Howard, Mark; Mansfield, Shane; Royal Society; Irish Research Council; Science Foundation IrelandRandom access codes have provided many examples of quantum advantage in communication, but concern only one kind of information retrieval task. We introduce a related task – the Torpedo Game – and show that it admits greater quantum advantage than the comparable random access code. Perfect quantum strategies involving prepare-and-measure protocols with experimentally accessible three-level systems emerge via analysis in terms of the discrete Wigner function. The example is leveraged to an operational advantage in a pacifist version of the strategy game Battleship. We pinpoint a characteristic of quantum systems that enables quantum advantage in any bounded- memory information retrieval task. While preparation contextuality has previously been linked to advantages in random access coding we focus here on a different characteristic called sequential contextuality. It is shown not only to be necessary and sufficient for quantum advantage, but also to quantify the degree of advantage. Our perfect qutrit strategy for the Torpedo Game entails the strongest type of inconsistency with non-contextual hidden variables, revealing logical paradoxes with respect to those assumptions.Publication Models of fractional viscous stresses for incompressible materials(SAGE Publications, 2024-03-13) Berjamin, Harold; Destrade, MichelWe present and review several models of fractional viscous stresses from the literature, which generalise classical viscosity theories to fractional orders by replacing total strain derivatives in time with fractional time derivatives. We also briefly introduce Prony-type approximations of these theories. Here, we investigate the issues of material frame-indifference and thermodynamic consistency for these models and find that on these bases, some are physically unacceptable. Next, we study elementary shearing and tensile motions, observing that some models are more convenient to use than others for the analysis of creep and relaxation. Finally, we compute the incremental stresses due to small-amplitude wave propagation in a deformed material, with a view to establish acoustoelastic formulas for prospective experimental calibrations.Publication Designing necks and wrinkles in inflated auxetic membranes(Elsevier, 2024-01-19) Venkata, Sairam Pamulaparthi; Balbi, Valentina; Destrade, Michel; Zurlo, GiuseppeThis article presents the potentiality of inflatable, functionally-graded auxetic membranes to produce wrinkles and necks. We obtain elastic instabilities at desired locations in axisymmetric membranes and with prescribed patterns in square membranes. First, we use an analytical approach to obtain a series of universal results providing insights into the formation of wrinkles and necks in inflated, axisymmetric membranes. For example, we prove analytically that necks and wrinkles may never overlap in pressurized, axially symmetric membranes. Second, we implement the relaxed strain energy of tension field theory into a Finite Element solver (COMSOL). By tuning spatial inhomogeneities of the material moduli, we corroborate our universal results, describe the onset of wrinkling in an averaged way, and also generate non-trivial instabilities at desired locations. This study on membranes with morphing or corrugation on demand has potential applications in Braille reading and haptics.Publication Singular travelling waves in soft viscoelastic solids of rate type(Elsevier, 2023-09-25) Berjamin, Harold; Destrade, Michel; Saccomandi, Giuseppe; Horizon 2020We consider shear wave propagation in soft viscoelastic solids of rate type. Based on objective stress rates, the constitutive model accounts for finite strain, incompressibility, as well as stress- and strain-rate viscoelasticity. The theory generalises the standard linear solid model to three-dimensional volume-preserving motions of large amplitude in a physically-consistent way. The nonlinear equations governing shear motion take the form of a one-dimensional hyperbolic system with relaxation. For specific objective rates of Cauchy stress (lower- and upper-convected derivatives), we study the propagation of acceleration waves and shock waves. Then we show that both smooth and discontinuous travelling wave solutions can be obtained analytically. We observe that the amplitude and velocity of steady shocks are very sensitive to variations of the stress relaxation time. Furthermore, the existence of steady shocks is conditional. Extension of these results to the case of multiple relaxation mechanisms and of the Jaumann stress rate is attempted. The analysis of simple shearing motions is more involved in these cases.Publication An atlas of the heterogeneous viscoelastic brain with local power-law attenuation synthesised using Prony-series(Elsevier, 2023-09-13) Morrison, Oisín; Destrade, Michel; Tripathi, Bharat B.This review addresses the acute need to acknowledge the mechanical heterogeneity of brain matter and to accurately calibrate its local viscoelastic material properties accordingly. Specifically, it is important to compile the existing and disparate literature on attenuation power-laws and dispersion to make progress in wave physics of brain matter, a field of research that has the potential to explain the mechanisms at play in diffuse axonal injury and mild traumatic brain injury in general. Currently, viscous effects in the brain are modelled using Prony-series, i.e., a sum of decaying exponentials at different relaxation times. Here we collect and synthesise the Prony-series coefficients appearing in the literature for twelve regions: brainstem, basal ganglia, cerebellum, corona radiata, corpus callosum, cortex, dentate gyrus, hippocampus, thalamus, grey matter, white matter, homogeneous brain, and for eight different mammals: pig, rat, human, mouse, cow, sheep, monkey and dog. Using this data, we compute the fractional-exponent attenuation power-laws for different tissues of the brain, the corresponding dispersion laws resulting from causality, and the averaged Prony-series coefficients.Publication Programmable wrinkling for functionally-graded auxetic circular membranes(Elsevier, 2023-07-13) Venkata, Sairam Pamulaparthi; Balbi, Valentina; Destrade, Michel; Accoto, Dino; Zurlo, Giuseppe; Horizon 2020Materials with negative Poisson¿s ratio, also known as auxetic materials, display exotic properties such as expansion in all directions under uni-axial tension. For their unique properties, these materials find a broad range of applications in robotic, structural, aerospace, and biomedical engineering. In this work we study the wrinkling behavior of thin and soft auxetic membranes, subjected to edge tractions. We show that spatial inhomogeneities of the Young modulus and of the Poisson ratio can be suitably tailored to produce non-trivial wrinkling patterns, with wrinkled regions that can appear, broaden, merge, and eventually disappear again, as the magnitude of applied tractions is increased monotonically. To model wrinkling in a functionally graded membrane, we employ the mathematically elegant and physically transparent tension field theory, an approximated method that we implement in commercially available software. Beyond unveiling the challenging technological potential to achieve non-standard wrinkling on demand in auxetic membranes, our study also confirms the potential of using tension field theory to study, analytically and numerically, instabilities in functionally graded materials.Publication Assessing ISO 18404 standard applicability in the service sector: a qualitative study(Emerald, 2024-01-18) Cudney, Elizabeth; Sony, Michael; Ramadan, Mariam Ali; Antony, Jiju; Al Dhaheri, Maha Khalifa; McDermott, Olivia; Cudney, Elizabeth A.This research aims to establish the applicability of the International Organisation for Standardisation (ISO) 18404 standard to the service sector, identify any required amendments and identify the critical success factors and barriers to deploying the standard within the service sector. Design/methodology/approach The study used a qualitative approach by interviewing operational excellence (OPEX) professionals who work in the service sector. Findings The findings indicate a significant lack of knowledge about the existence of the standard and a general scepticism regarding the applicability of the current ISO 18404 standard to the service sector. Research limitations/implications Limited examples of the application of ISO 18404 in organisations exist, as only a few organisations have adopted the standard. Therefore, the research focussed on the challenges and obstacles that experienced OPEX professionals perceived could be an issue. Originality/value The study will aid service sector organisations in understanding the standard and, subsequently, determine whether to pursue it as part of an OPEX programme. This research is the first study on the application of ISO 18404 to the service sector.Publication Global perspectives on operational excellence: unveiling critical failure factors and sustainable pathways(Emerald, 2024-03-14) Antony, Jiju; Sony, Michael; Jayaraman, Raja; Swarnakar, Vikas; Tortorella, Guilherme da Luz; Garza-Reyes, Jose Arturo; Rathi, Rajeev; Gutierrez, Leopoldo; McDermott, Olivia; Lameijer, Bart AlexPurpose The purpose of this global study is to investigate the critical failure factors (CFFs) in the deployment of operational excellence (OPEX) programs as well as the key performance indicators (KPIs) that can be used to measure OPEX failures. The study also empirically analyzes various OPEX methodologies adopted by various organizations at a global level. Design/methodology/approach This global study utilized an online survey to collect data. The questionnaire was sent to 800 senior managers, resulting in 249 useful responses. Findings The study results suggest that Six Sigma is the most widely utilized across the OPEX methodologies, followed by Lean Six Sigma and Lean. Agile manufacturing is the least utilized OPEX methodology. The top four CFFs were poor project selection and prioritization, poor leadership, a lack of proper communication and resistance to change issues. Research limitations/implications This study extends the current body of knowledge on OPEX by first delineating the CFFs for OPEX and identifying the differing effects of these CFFs across various organizational settings. Senior managers and OPEX professionals can use the findings to take remedial actions and improve the sustainability of OPEX initiatives in their respective organizations. Originality/value This study uniquely identifies critical factors leading to OPEX initiative failures, providing practical insights for industry professionals and academia and fostering a deeper understanding of potential pitfalls. The research highlights a distinctive focus on social and environmental performance metrics, urging a paradigm shift for sustained OPEX success and differentiating itself in addressing broader sustainability concerns. By recognizing the interconnectedness of 12 CFFs, the study offers a pioneering foundation for future research and the development of a comprehensive management theory on OPEX failures.Publication Canceling the elastic Poynting effect with geometry(American Physical Society, 2023-05-24) Destrade, Michel; Du, Y.; Blackwell, J.; Colgan, N.; Balbi, V.; Irish Research CouncilThe Poynting effect is a paragon of nonlinear soft matter mechanics. It is the tendency (found in all incompressible, isotropic, hyperelastic solids) exhibited by a soft block to expand vertically when sheared horizontally. It can be observed whenever the length of the cuboid is at least four times its thickness. Here we show that the Poynting effect can be easily reversed and the cuboid can shrink vertically, simply by reducing this aspect ratio. In principle, this discovery means that for a given solid, say one used as a seismic wave absorber under a building, an optimal ratio exists where vertical displacements and vibrations can be completely eliminated. Here we first recall the classical theoretical treatment of the positive Poynting effect, and then show experimentally how it can be reversed. Using finite-element simulations, we then investigate how the effect can be suppressed. We find that cubes always provide a reverse Poynting effect, irrespective of their material properties (in the third-order theory of weakly nonlinear elasticity).Publication Noninvasive measurement of local stress inside soft materials with programmed shear waves(American Association for the Advancement of Science, 2023-03-08) Zhang, Zhaoyi; Li, Guo-Yang; Jiang, Yuxuan; Zheng, Yang; Gower, Artur L.; Destrade, Michel; Cao, Yanping; Horizon 2020Mechanical stresses across different length scales play a fundamental role in understanding biological systems¿ functions and engineering soft machines and devices. However, it is challenging to noninvasively probe local mechanical stresses in situ, particularly when the mechanical properties are unknown. We propose an acoustoelastic imaging¿based method to infer the local stresses in soft materials by measuring the speeds of shear waves induced by custom-programmed acoustic radiation force. Using an ultrasound transducer to excite and track the shear waves remotely, we demonstrate the application of the method by imaging uniaxial and bending stresses in an isotropic hydrogel and the passive uniaxial stress in a skeletal muscle. These measurements were all done without the knowledge of the constitutive parameters of the materials. The experiments indicate that our method will find broad applications, ranging from health monitoring of soft structures and machines to diagnosing diseases that alter stresses in soft tissues.Publication Analysis of in vivo skin anisotropy using elastic wave measurements and Bayesian modelling(Springer, 2023-04-06) Nagle, Matt; Price, Susan; Trotta, Antonia; Destrade, Michel; Fop, Michael; Ní Annaidh, AislingIn vivo skin exhibits viscoelastic, hyper-elastic and non-linear characteristics. It is under a constant state of non-equibiaxial tension in its natural configuration and is reinforced with oriented collagen fibers, which gives rise to anisotropic behaviour. Understanding the complex mechanical behaviour of skin has relevance across many sectors including pharmaceuticals, cosmetics and surgery. However, there is a dearth of quality data characterizing the anisotropy of human skin in vivo. The data available in the literature is usually confined to limited population groups and/or limited angular resolution. Here, we used the speed of elastic waves travelling through the skin to obtain measurements from 78 volunteers ranging in age from 3 to 93 years old. Using a Bayesian framework allowed us to analyse the effect that age, gender and level of skin tension have on the skin anisotropy and stiffness. First, we propose a new measurement of anisotropy based on the eccentricity of angular data and conclude that it is a more robust measurement when compared to the classic ¿anisotropic ratio¿. Our analysis then concluded that in vivo skin anisotropy increases logarithmically with age, while the skin stiffness increases linearly along the direction of Langer Lines. We also concluded that the gender does not significantly affect the level of skin anisotropy, but it does affect the overall stiffness, with males having stiffer skin on average. Finally, we found that the level of skin tension significantly affects both the anisotropy and stiffness measurements employed here. This indicates that elastic wave measurements may have promising applications in the determination of in vivo skin tension. In contrast to earlier studies, these results represent a comprehensive assessment of the variation of skin anisotropy with age and gender using a sizeable dataset and robust modern statistical analysis. This data has implications for the planning of surgical procedures and questions the adoption of universal cosmetic surgery practices for very young or elderly patients.Publication Voltage-controlled topological interface states for bending waves in soft dielectric phononic crystal plates(Elsevier, 2022-11-19) Chen, Yingjie; Wu, Bin; Destrade, Michel; Chen, Weiqiu; Horizon 2020The operating frequency range of passive topological phononic crystals is generally fixed and narrow, limiting their practical applications. To overcome this difficulty, here we design and investigate a one-dimensional soft dielectric phononic crystal (PC) plate system with actively tunable topological interface states via the mechanical and electric loads. We use nonlinear electroelasticity theory and linearized incremental theory to derive the governing equations. First we determine the nonlinear static response of the soft dielectric PC plate subjected to a combination of axial force and electric voltage. Then we study the motion of superimposed incremental bending waves. By adopting the Spectral Element Method, we obtain the dispersion relation for the infinite PC plate and the transmission coefficient for the finite PC plate waveguide. Numerical results show that the low-frequency topological interface state exists at the interface of the finite phononic plate waveguide with two topologically different elements. By simply adjusting the axial force or the electric voltage, an increase or decrease in the frequency of the topological interface state can be realized. Furthermore, applying the electric voltage separately on different elements of the PC plate waveguide is a flexible and smart method to tune the topological interface state in a wide range. These results provide guidance for designing soft smart wave devices with low-frequency tunable topological interface states.Publication Non-destructive mapping of stress and strain in soft thin films through sound waves(Nature Research, 2022-09-17) Li, Guo-Yang; Gower, Artur L.; Destrade, Michel; Yun, Seok-HyunMeasuring the in-plane mechanical stress in a taut membrane is challenging, especially if its material parameters are unknown or altered by the stress. Yet being able to measure the stress is of fundamental interest to basic research and practical applications that use soft membranes, from engineering to tissues. Here, we present a robust non-destructive technique to measure directly in-situ stress and strain in soft thin films without the need to calibrate material parameters. Our method relies on measuring the speed of elastic waves propagating in the film. Using optical coherence tomography, we verify our method experimentally for a stretched rubber membrane, a piece of cling film (about 10 ¿m thick), and the leather skin of a traditional Irish frame drum. We find that our stress predictions are highly accurate and anticipate that our technique could be useful in applications ranging from soft matter devices to biomaterial engineering and medical diagnosis.Publication Representing the stress and strain energy of elastic solids with initial stress and transverse texture anisotropy.(The Royal Society, 2022-10-12) Mukherjee, Soumya; Destrade, Michel; Gower, Artur L.Real-world solids, such as rocks, soft tissues and engineering materials, are often under some form of stress. Most real materials are also, to some degree, anisotropic due to their microstructure, a characteristic often called the `texture anisotropy¿. This anisotropy can stem from preferential grain alignment in polycrystalline materials, aligned micro-cracks or structural reinforcement, such as collagen bundles in biological tissues, steel rods in pre-stressed concrete and reinforcing fibres in composites. Here, we establish a framework for initially stressed solids with transverse texture anisotropy. We consider that the strain energy per unit mass of the reference is an explicit function of the elastic deformation gradient, the initial stress tensor and the texture anisotropy. We determine the corresponding constitutive relations and develop examples of nonlinear strain energies that depend explicitly on the initial stress and direction of texture anisotropy. As an application, we then employ these models to analyse the stress distribution of an inflated initially stressed cylinder with texture anisotropy and the tension of a welded metal plate. We also deduce the elastic moduli needed to describe linear elasticity from stress reference with transverse texture anisotropy. As an example, we show how to measure the stress with small-amplitude shear waves.